Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1991 Geo Tracker LSi, AutomaticFACTORY OEM SERVICE PROCEDURE
Retrieving Codes
- Using a jumper wire, connect Blue/Yellow and Black wires of diagnostic connector. Diagnostic connector is located in engine compartment, near battery. See Fig 1 . Turn ignition switch to ON position. Read fault code(s). Proceed to appropriate chart(s) under DIAGNOSTIC CODE CHARTS to diagnose fault codes.
- If no fault codes are stored, CHECK ENGINE light will flash on and off rapidly until jumper wire is removed. Count the number of flashes and look for pauses in flashing to ensure no fault codes are overlooked. If fault codes are stored, code will flash 3 times starting with the lowest code.
FAULT CODE IDENTIFICATION
| Code | Circuit Affected | Probable Cause | ||
|---|---|---|---|---|
| 13 | Oxygen Sensor | Open Circuit | ||
| 14 | Coolant Temp. Sensor | Low Temp. Indicated | ||
| 15 | Coolant Temp. Sensor | High Temp. Indicated | ||
| 21 | Throttle Switch | Idle Switch & Throttle Switch Are On | ||
| 21 | Throttle Position Sensor | Signal Voltage High | ||
| 22 | Throttle Position Sensor | Signal Voltage Low | ||
| 23 | Intake Air Temp. Sensor | Low Temp. Indicated | ||
| 24 | Vehicle Speed | Incorrect Signal Voltage | ||
| 25 | Intake Air Temp. Sensor | High Temp. Indicated | ||
| 31 | MAP Sensor | Signal Voltage High, Low Voltage | ||
| 32 | MAP Sensor | Signal Voltage Low, High Vacuum | ||
| 41 | Ignition Signal | No Signal | ||
| 42 | Crank Angle Sensor | No Signal | ||
| 44 | Idle Switch | Open/Misadjusted TPS | ||
| 45 | Idle Switch | Ground/Misadjusted TPS | ||
| 51 (1) | EGR System | Out Of Calibration | ||
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Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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